Hush! Say not the word of that manga or we will soon see... *gasp* FANBOYS!

All anime have fillers - it's unavoidable. For fillers to start on the 13th episode could mean that they're randomly inserted between actual plot, which could be good because that means that they won't be long plot arcs that have to be remembered later. It's not a shoujo, which means that it'll probably go back to the manga plot at some point.

And I hope D.Gray-Man goes as long/longer than Bleach, anyway - the manga, that is. ^_^